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Posts Tagged: catalytic converter code

P0420 Catalyst System Efficiency

P0420 Catalyst System Efficiency Below Threshold (Bank 1) Code P0420 Catalyst System Efficiency Below Threshold (Bank 2) NOTE: Codes P0420 and code P0430 are similar. I wrote a much more detailed explanation of how an emission system works and what causes these codes. Read this post and then refer to this more detailed post. Code P0420 means the catalytic converter for bank 1 has failed it’s testing. The oxygen sensor in front of the catalytic converter switches back and forth between rich and lean as the computer constantly changes air … Read More


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